Former Stanford lineman Jonathan Martin left the Dolphins on Monday to receive help for emotional issues.(USATSI)

MIAMI -- The NFL Players Association will investigate possible harassment of Miami Dolphins tackle Jonathan Martin by his teammates, a person familiar with the situation said Saturday.

The person said the union wants to determine whether Martin's treatment by teammates contributed to his abrupt departure from the Dolphins. The person spoke to The Associated Press on condition of anonymity because the Dolphins have said little about the reasons for Martin's absence.

Martin left the team Monday to receive help for emotional issues, and it's unclear whether or when he's expected back. The Dolphins are off this weekend, and the union plans to look into the matter next week.

The Dolphins have attributed Martin's absence to a non-football illness. The second-year pro from Stanford played in Sunday's loss at New England, then missed practice this week and sat out Thursday night's victory over Cincinnati.

The win snapped a four-game losing streak that had stirred talk of dissension between coaches and among players. When asked Friday if he has seen evidence of bullying or harassment, coach Joe Philbin said: ''This is something we take very seriously, and it will not be tolerated.''